1. Field of the Invention
This invention relates to methods for determining or predicting response to cancer therapy in an individual. The invention also relates to methods for using image analysis of immunohistochemically-stained tissue biopsies to quantify c-kit/SCF/pAKT expression and activation, and to identify efficacious anticancer compounds.
2. Background of the Invention
A primary goal of cancer therapy is to selectively kill or inhibit uncontrolled growth of malignant cells while not adversely affecting normal cells. Traditional chemotherapeutic drugs are highly cytotoxic agents that preferably have greater affinity for malignant cells than for normal cells, or at least preferentially affect malignant cells based on their high rate of cell growth and metabolic activity. However, these agents often harm normal cells.
Generally, anticancer drugs, monoclonal antibodies, chemotherapeutic or chemopreventive agents are used to produce growth arrest, terminal differentiation and cell death of the cancerous or precancerous cells (Mendelsohn, 1990, Semin. Cancer Biol. 1:339-44; Hancock et al., 1991, Cancer Res. 51:4575-80; Arteaga et al., 1994, Cancer Res., 54:3758-65; Pietras et al., 1994, Oncogene 9:1829-38; Bacus et al., 1997, Anal. Quant. Cytol. Histol. 19:316-28; Bacus et al., 1999, Breast J.; Baselga et al., 1999, Proceedings of AACR NCI EORTC International Conference, Abstract 98; Cobleigh et al., 1999, J. Clin. Oncol. 17:2639-48; DiGiovanna, 1999, PPO Updates: Princ. Practice Oncol. 13:1-9; Hortobagyi, 1999, J. Clin. Oncol. 17:25-29; Shak, 1999, Semin. Oncol. 26:71-77; Sliwkowski et al., 1999, Semin. Oncol. 26:60-70; Vincent et al., 2000, Cancer Chemother. Pharmacol. 45: 231-38). Drug-induced growth arrest or cell death is often characterized by morphological and biochemical changes associated with programmed cell death or terminal differentiation (as opposed to mitotic cell death).
Although chemotherapeutic drugs can be administered at doses high enough to bring about cell death, such doses typically produce deleterious effects on normal as well as tumor cells. Differentiating agents, and the use of lower doses of chemotherapeutic drugs and agents frequently results in growth arrest rather than cell death. Such growth arrest can be followed by apoptosis and cell death, or continued proliferation once the chemotherapeutic drugs are withdrawn. Administration of cytotoxic and chemotherapeutic drugs or ionizing radiation may also induce transient growth arrest, a state that depends largely on the function of p53 and p53-regulated cyclin-dependent kinase inhibitors (such as p16, p27, and p19) or growth inhibitors (such as TGF-β, IL-4, and IL-6). Upon removal of the chemotherapeutic drug, cells subjected to the drug treatment will eventually resume division and either continue to proliferate or die. Some drug-treated tumor cells undergo prolonged growth arrest and fail to resume cell division upon release from the drug.
Apoptosis is generally regarded as an active suicide response to various physiological or pathological stimuli. Recent studies have shown that a variety of DNA-damaging agents, including X-ray irradiation and several chemotherapeutic drugs (e.g., alkylating agents and topoisomerase II inhibitors) initiate pathways leading to apoptosis. The exact mechanism by which apoptosis is induced by these agents is not yet known. However, expression of the tumor suppressor gene p53 has been implicated in this process (Kwok and Sutherland, 1989, J. Natl. Cancer Inst. 81:1020-24; Kwok and Sutherland, 1991, Int. J. Cancer 49:73-76; Lane, 1992, Nature 358:15-16; Kuerbitz et al., 1992, Proc. Natl. Acad. Sci. U.S.A. 89:7491-95; Luo et al., 1995, Nature 375:159-61; Liu et al., 1996, Cancer Res. 56:31-35; Mellinghoff and Sawyers, 2000, PPO Updates 14:1-11). In addition, the up-regulation of caspases (e.g., caspase 9 or caspase 3) or their chaperone molecules (e.g., heat shock protein 60) has been associated with apoptosis.
Cells can be rendered resistant to apoptosis in a variety of ways, including deletion of cellular genes such as the tumor suppressor gene PTEN, overexpression of active Ras, and overexpression of active PI3K. A particular cellular protein, AKT (the protein product of the c-akt gene) has been identified as a key regulator of cellular survival and an inhibitor of apoptosis, which has significant implications for oncogenesis and drug resistance. For example, the loss of PTEN correlates with increased AKT activity (Li et al., 1997, Science 275:1943-47; Liaw et al., 1997, Nat. Genet. 16:64-67; Nelen et al., 1997, Hum. Mol. Genet. 6:1383-87; Cantley and Neel, 1999, Proc. Natl. Acad. Sci. U.S.A. 96:4240-45; Datta et al., 1999, Genes Dev. 13:2905-27). In addition, suppression of apoptosis is not the only function that AKT may have in promoting oncogenesis. In some circumstances, AKT can also induce cell cycle progression. However, the observation that AKT can suppress apoptosis suggests that oncogenes may block adaptive cellular apoptosis by hyperactivating AKT.
Given the complexity of the apoptotic machinery, there are a number of pathways by which AKT might act to promote cell survival and inhibit cell death. AKT may block apoptosis by regulating expression or activity of members of Bcl-2 gene family (that are known to play a role in cell survival or cell death). Alternatively, AKT may regulate expression or activity of the caspase family of proteins, or the function of death receptor pathways. The regulatory effect of AKT may be through a direct mechanism—the phosphorylation of components of the apoptotic machinery, for example—or an indirect mechanism—such as by altering the expression level of genes that encode components of the death machinery. Recent studies suggest that AKT regulates apoptosis at multiple sites. A number of AKT targets, all playing critical roles in mediating cell death, have been identified, including BAD, caspase-9, the Forkhead family of transcription factors, and the NFκB regulator IKK (Datta et al., 1999, supra).
The c-kit proto-oncogene encodes a transmembrane tyrosine kinase growth factor receptor that is placed in the same class as the receptors for PDGF and CSF-1 by virtue of their similar immunoglobulin-like extracellular domains and the interruptions of their cytoplasmic tyrosine kinase domain by a hydrophilic insert. (Yarden et al., 1987, EMBO J. 6:3341-3351). Its ligand, known alternatively as stem cell growth factor (“SCF”), mast cell growth factor, kit ligand, or steel factor, is an early hematopoietic growth factor that, in conjunction with other growth factors, supports the proliferation and differentiation of multiple hematopoietic lineages. Id.
In several small-cell lung cancer cell lines and breast cancer cell lines, it has been demonstrated that co-expression of c-kit and SCF occurs, suggesting that autocrine growth stimulation may play a role in non-hematopoietic tumors. Autocrine growth requires co-expression of SCF and c-kit. In two independent studies, immunostaining of frozen sections using polyclonal antisera directed against the carboxyl terminus of c-kit has demonstrated uniformly strong staining of normal breast ductal epithelial cells. These studies also demonstrated that, using the same methodology, at least 10-20% of breast carcinomas retain c-kit expression. Neither of these studies, however, addressed the expression of SCF in breast tumors. It is possible, therefore, that the co-expression of c-kit and SCF could play a role in the growth regulation of some breast tumors. (Hines, et al., 1995, Cell Growth & Differentiation, 6:769-779; Natali et al., 1992, Int. J. Cancer, 52:713-717; Chui et al, 1996, British J. of Cancer, 73:1233-1236). In addition, co-expression of c-kit and other growth factors in breast cancer results in enhanced sensitivity to the EGF family of growth factors. (Hines et al., 1999, Breast Cancer Research and Treatment 58: 1-10).
Therefore, there exists a need in the art for improved detection of expression and activation of proteins and ligands that are directly or indirectly responsible for the expression or activation of AKT. There is also a need for improved detection of expression and activation of c-kit and expression of its ligand SCF.